Method and Apparatus of In-Loop Filtering for Virtual Boundaries

ABSTRACT

Method and apparatus of coding a video sequence are disclosed. According to this method, a first syntax is signalled in or parsed from a bitstream, where the first syntax indicates whether a loop filtering process is disabled for one or more virtual boundaries in a corresponding region. A reconstructed filter unit in a current picture is received, wherein the reconstructed filter unit is associated with the loop filter and the reconstructed filter unit comprises reconstructed pixels for applying a loop filtering process associated with the loop filter to a current reconstructed pixel. When the first syntax is true, the loop filter processing is disabled when the reconstructed filter unit is across said one or more virtual boundaries in the corresponding region. When the first syntax is false, the loop filter processing is not disabled when the reconstructed filter unit is across the virtual boundary.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention claims priority to U.S. Provisional PatentApplication, Ser. No. 62/791,963, filed on Jan. 14, 2019 and U.S.Provisional Patent Application, Ser. No. 62/792,489, filed on Jan. 15,2019, and PCT Serial No. PCT/CN2019/128631, filed on Dec. 26, 2019. TheU.S. Provisional Patent Applications are hereby incorporated byreference in their entireties.

FIELD OF THE INVENTION

The present invention relates to picture processing for picturescontaining one or more virtual boundaries such as 360-degree virtualreality (VR360) pictures. In particular, the present invention relatesto syntax design for in-loop filtering process at discontinued edges orvirtual boundaries for pictures containing one or more virtualboundaries such as VR360 video.

BACKGROUND AND RELATED ART

The 360-degree video, also known as immersive video is an emergingtechnology, which can provide “feeling as sensation of present”. Thesense of immersion is achieved by surrounding a user with wrap-aroundscene covering a panoramic view, in particular, 360-degree field ofview. The “feeling as sensation of present” can be further improved bystereographic rendering. Accordingly, the panoramic video is beingwidely used in Virtual Reality (VR) applications.

The 360-degree virtual reality (VR) pictures may be captured using a360-degree spherical panoramic camera or multiple pictures arranged tocover all field of views around 360 degrees. The three-dimensional (3D)spherical picture is difficult to process or store using theconventional picture/video processing devices. Therefore, the 360-degreeVR pictures are often converted to a two-dimensional (2D) format using a3D-to-2D projection method, such as EquiRectangular Projection (ERP) andCubeMap Projection (CMP). Besides the ERP and CMP projection formats,there are various other VR projection formats, such as OctaHedronProjection (OHP), icosahedron projection (ISP), Segmented SphereProjection (SSP) and Rotated Sphere Projection (RSP) that are widelyused in the field.

The VR360 video sequence usually requires more storage space than theconventional 2D video sequence. Therefore, video compression is oftenapplied to VR360 video sequence to reduce the storage space for storageor the bit rate for streaming/transmission.

The High Efficiency Video Coding (HEVC) standard is developed under thejoint video project of the ITU-T Video Coding Experts Group (VCEG) andthe ISO/IEC Moving Picture Experts Group (MPEG) standardizationorganizations, and is especially with partnership known as the JointCollaborative Team on Video Coding (JCT-VC). VR360 video sequences canbe coded using HEVC. However, the present invention may also beapplicable for other coding methods.

In HEVC, one slice is partitioned into multiple coding tree units (CTU).For colour pictures, a colour slice may be partitioned into multiplecoding tree blocks (CTB). The CTU is further partitioned into multiplecoding units (CUs) to adapt to various local characteristics. HEVCsupports multiple Intra prediction modes and for Intra coded CU, theselected Intra prediction mode is signalled. In addition to the conceptof coding unit, the concept of prediction unit (PU) is also introducedin HEVC. Once the splitting of CU hierarchical tree is done, each leafCU is further split into one or more prediction units (PUs) according toprediction type and PU partition. After prediction, the residuesassociated with the CU are partitioned into transform blocks, namedtransform units (TUs) for the transform process.

While the coding process can effectively reduce required bandwidth fortransmission or required capacity for storage, the coding process oftenintroduces coding noise referred as coding artefacts. In order toalleviate the coding artefact, various filtering techniques, such asde-blocking filter, SAO (sample adaptive offset) and ALF (adaptive loopfilter), have been introduced. The filtering process is often applied toreconstructed pictures that are later used as reference pictures. Inother words, the filtering process is inside the coding loop.Accordingly, such filtering process is also referred as in-loopfiltering.

In HEVC, de-blocking filter is applied after the picture isreconstructed. The boundaries between coding units, prediction units ortransform units are filtered to alleviate the blocking artefacts causedby the block-based coding. The boundary can be a vertical or horizontalboundary. The boundary pixels involved in de-blocking filtering processfor the vertical boundary (110) and horizontal boundary (120) as shownin FIG. 1A and FIG. 1B respectively. For a vertical boundary (i.e., line110 in FIG. 1A), a horizontal filter is applied to some boundary samplesin each horizontal line. For example, the horizontal de-blocking filtermay be applied to p00, p01 and p02 on the left side of the verticalboundary and q00, q01 and q02 on the right side of the verticalboundary. Similarly, for a horizontal boundary (i.e., line 120 in FIG.1B), a vertical filter is applied to some boundary samples in eachvertical line. For example, the vertical de-blocking filter may beapplied to p00, p01 and p02 on the top side of the horizontal boundaryand q00, q01 and q02 on the bottom side of the horizontal boundary. Inother words, the de-blocking filter is applied in a directionperpendicular to the boundary.

A boundary strength value, Bs is calculated for each four-sample lengthboundary and can take 3 possible values. Luma and chroma components areprocessed separately in the de-blocking process. For the Luma component,only block boundaries with Bs values equal to 1 or 2 can be filtered. Inthe case of chroma components, only boundaries with Bs value equal to 2can be filtered.

For luma component, additional conditions are checked for eachfour-sample length boundary to determine whether de-blocking filteringshould be applied and to further determine whether a normal filter or astrong filter should be applied if de-blocking is applied.

For the luma component in the normal filtering mode, two samples at eachside of the boundary can be modified. In the strong filtering mode,three samples at each side of the boundary can be modified.

For the chroma component, only one sample at each side of the boundarycan be modified when the boundary strength is greater than 1.

SAO processing is developed to compensate intensity level offset causedby the coding process. SAO processing adopted by HEVC consists of twomethods. One is Band Offset (BO), and the other is Edge Offset (EO). BOis used to classify pixels into multiple bands according to pixelintensities and an offset is applied to pixels in one or more bands. EOis used to classify pixels into categories according to relationsbetween a current pixel and respective neighbours and an offset isapplied to pixels in each category. There are 4 EO directional patterns(0°, 90°, 135°, and 45°) and no processing (OFF). The four EO types areshown in FIG. 2.

Upon classification of all pixels in a region, one offset is derived andtransmitted for pixels in each category. SAO processing is applied toluma and chroma components, and each of the components is independentlyprocessed. One offset is derived for all pixels of each category exceptfor category 4 of EO, where Category 4 is forced to use zero offset.Table 1 below lists the EO pixel classification, where “C” denotes thepixel to be classified. As shown in Table 1, the conditions associatedwith determining a category are related to comparing the current pixelvalue with two respective neighbour values according to the EO type. Thecategory can be determined according to the comparison results (i.e.,“>”, “<” or “=”). Each category has a special meaning in relativeintensity between the current pixel and neighbouring pixels. Forexample, category 0 corresponds to a “valley”, where the intensity ofthe centre pixel is lower than two neighbouring pixels. Category 3corresponds to a “peak”, where the intensity of the centre pixel ishigher than two neighbouring pixels. Categories 1 and 2 correspond to aflat segment with an upward slope (Category 2) or a downward slope(Category 1).

TABLE 1 Category Condition 0 C < two neighbours 1 C < one neighbour && C== one neighbour 2 C > one neighbour && C == one neighbour 3 C > twoneighbours 4 None of the above

Adaptive Loop Filter (ALF) is a filter with adaptive filter size appliedto the reconstructed pixels. ALF was evaluated during the HEVC standarddevelopment, but not adopted for HEVC. However, ALF is being consideredby the emerging video coding standard, named VVC (Versatile VideoCoding). To optimize the performance, ALF uses Wiener filteringtechniques to derive filter coefficients. Furthermore, multiple filtersare allowed for different picture regions. For example, the ALF can be a5×5 filter or a 7×7 filter as shown in FIG. 3, where “C” indicates acurrent reconstructed pixel being filtered.

According to a conventional approach, the loop filters such asde-blocking, SAO and ALF will be applied to a reconstructed VR360picture without considering the possible discontinued edges within theVR360 picture. For example, the cubemap based projection uses six faceson a cube to represent one frame in the VR360 video. The six facescorresponds to faces lifted off from the cube and fitted into differentlayouts, such as 1×6, 6×1, 2×3 or 3×2 layout. Among various cubemaplayouts, the 3×2 layout is often used due to its coding efficiency. FIG.4 illustrates an example of 3×2 cubemap layout formation. The layout 410corresponds to six faces lifted off from a cube, where image 412corresponds to a front face, the three images 414 connected to the leftof image 412 correspond to the other three faces connected to the frontface 412 in the horizontal direction, image 416 corresponds to the faceon the top of the cube and image 418 corresponds to the face on thebottom of the cube. Accordingly, the fours images including images 414and image 412 are continuous in the horizontal direction and the threeimages includes image 416, image 412 and image 418 are continuous in thevertical direction. The 4×3 layout 410 contains some blank areas, whichis not efficient for coding. The layout 420 corresponds to a 3×2 cubemaplayout, where the three images 414 and the three vertically connectedimages (images 416, 412 and 418) are abutted. The top sub-framecorresponding to the three images 414 are continuous in the horizontaldirection. Also, the bottom sub-frame corresponding to the three images412, 416 and 418 are continuous in the horizontal direction. However,the edges 422 between the top sub-frame and the bottom sub-frame isdiscontinuous. In other words, a VR360 picture corresponding to a layoutformat from a 3D projection may contain discontinuous edge within thepicture.

Besides the VR360 pictures, other picture formats may also containdiscontinuous edges within the picture. For example, thePicture-In-Picture (PIP) format is a popular format to display twovideos (e.g. a main video and a sub-video) on the same screensimultaneously. Therefore, for each PIP frame, discontinuity may existbetween the pictures associated with the two videos. The issues of loopfiltering process across the discontinuous edge exist in the VR360pictures as well as the PIP frames.

FIG. 5A to FIG. 5C illustrate examples of in-loop filters applied to areconstructed VR360 picture. FIG. 5A illustrates an example ofde-blocking filter, where the de-blocking filter is applied to a currentblock 510. The de-blocking filter is applied to the horizontal boundary516 between the current block 510 and the neighbouring block 512 above.The de-blocking filter is also applied to the vertical boundary 518between the current block 510 and the neighbouring block 514 on theleft.

FIG. 5B illustrates an example of SAO processing. The offsetcompensation parameters are derived based on the statistics of eachcoding tree unit (CTU) 520. During the statistic derivation, the BO andEO classification is applied to all pixels. For each BO and EO category,an offset value is determined. After the statistics for the CTU arecollected, the SAO can be applied to reconstructed pixels in the CTU.

FIG. 5C illustrates an example of ALF process for a reconstructed VR360picture. A reconstructed pixel 530 may be filtered by a 5×5 filter or areconstructed pixel 532 may be filtered by a 7×7 filter. As mentionedbefore, the filter parameters may be designed using Wiener filtertechnique to minimize the error between the original picture and thereconstructed picture. For each reconstructed pixel, the filter size isadaptively selected to achieve the best performance.

As illustrated in layout 420 in FIG. 4, the 3×2 layout for cubemapcontains a discontinuous edge between the top sub-frame and the bottomsub-frame. The pixels on one side of the boundary 422 may be quitedifferent from the pixels on the other side of the boundary 422.Therefore, when an in-loop filter is applied to reconstructed pixelsnext to the boundary or close to the boundary, it may cause undesirableresult. FIG. 6 illustrates an example of SAO filter applied to areconstructed pixel 622, where the discontinuous edge 610 is indicated.SAO operation 620 at the discontinuous edge is illustrated for thereconstructed pixel 622. The 3×3 SAO window is indicated by thedash-lined box 624. For the horizontal boundary 610, the SAO filteringprocess for 90°, 135°, and 45° will utilise a reference pixel from theother side of the discontinuous boundary. The neighbouring pixels 626 onthe other side of discontinuous edge (named unexpected pixels) may bevery different from the reconstructed pixel 622 being filtered thoughthey are close to the reconstructed pixel 622. In this case, the SAOprocessing for the boundary pixels may produce undesirable results.

Therefore, it is desirable to develop techniques to overcome the issuesrelated to in-loop filter for VR360 pictures.

BRIEF SUMMARY OF THE INVENTION

Method and apparatus of coding a video sequence are disclosed, whereinthe reconstructed filter unit comprises a plurality of reconstructedpixels for loop filtering process. According to this method, a firstsyntax is signalled in a bitstream at an encoder side or the firstsyntax is parsed from the bitstream at a decoder side. A reconstructedfilter unit in a current picture is received, wherein the reconstructedfilter unit is associated with a loop filter and the reconstructedfilter unit comprises reconstructed pixels for applying a loop filteringprocess associated with the loop filter to a current reconstructedpixel. The first syntax indicates whether the loop filtering process isdisabled for one or more virtual boundaries in a corresponding region.When the first syntax is true, the loop filter processing is disabledwhen the reconstructed filter unit is across said one or more virtualboundaries in the corresponding region. When the first syntax is false,the loop filter processing is not disabled when the reconstructed filterunit is across the virtual boundary.

The first syntax can be signalled in or parsed from the bitstream at asyntax level comprising SPS (Sequence Parameter Set), PPS (PictureParameter Set), APS (Application Parameter Set), slice, tile, picture,CTU (Coding Tree Unit), CU (Coding Unit), PU (Prediction Unit) or TU(Transform Unit) level for the corresponding region.

In one embodiment, if the first syntax is true, one or more secondsyntaxes are signalled at the encoder side or parsed at the decoder sideto indicate virtual boundary information in the corresponding region.The second syntaxes comprise a first number to indicate a number ofvertical virtual boundaries and a second number to indicate a number ofhorizontal virtual boundaries in the corresponding region. In oneexample, each vertical virtual boundary is from a top edge to a bottomedge of the corresponding region and each horizontal virtual boundary isfrom a left edge to a right edge of the corresponding region. In thiscase, when the first number is greater than 0, locations of eachvertical virtual boundary are transmitted in or parsed from thebitstream. When the second number is greater than 0, locations of eachhorizontal virtual boundary are transmitted in or parsed from thebitstream.

In another example, the vertical virtual boundaries are not necessarilyfrom a top edge to a bottom edge of the corresponding region and thehorizontal virtual boundaries are not necessarily from a left edge to aright edge of the corresponding region. In this case when the firstnumber is greater than 0, locations of x-position, y starting positionand y ending position for each vertical virtual boundary are transmittedin or parsed from the bitstream; and when the second number is greaterthan 0, locations of y-position, x starting position and x endingposition for each horizontal virtual boundary are transmitted in orparsed from the bitstream.

In yet another example, length of the vertical virtual boundaries andthe length of the horizontal virtual boundaries is fixed. In this case,when the first number is greater than 0, location of starting point foreach vertical virtual boundary is transmitted in or parsed from thebitstream. When the second number is greater than 0, the location ofstarting point for each horizontal virtual boundary is transmitted in orparsed from the bitstream.

In one embodiment, if the first syntax is true, one or more secondsyntaxes are signalled at the encoder side or parsed at the decoderside, where said one or more second syntaxes indicate a number of saidone or more virtual boundaries in the corresponding region. When thenumber of said one or more virtual boundaries is greater than 0,locations of starting points and ending points of said one or morevirtual boundaries are transmitted in or parsed from the bitstream. Saidone or more virtual boundaries may correspond to one or more rectangleboxes and starting points and ending points correspond to left-toppositions and right-bottom positions of said one or more rectangleboxes.

In one embodiment, if the first syntax is true, a second syntax issignalled at the encoder side or parsed at the decoder side, and whereinsaid the second syntax indicates a shape of at least one virtualboundary in the corresponding region. For example, the shape of at leastone virtual boundary in the corresponding region comprises astraight-line virtual boundary and a circular virtual boundary. When thesecond syntax indicates a circular virtual boundary, one or more thirdsyntaxes are signalled at the encoder side or parsed at the decoder sideto indicate location of centre and radius of at least one circle.

In one embodiment, one or more second syntaxes are signalled at theencoder side or parsed at the decoder side to indicate difference valuesbetween a current virtual boundary and a previous virtual boundary. Forexample, when the current virtual boundary is a first virtual boundaryin the corresponding region, absolute position of the first virtualboundary is signalled directly at the encoder side or parsed directly atthe decoder side. In another example, when the current virtual boundaryis a first virtual boundary in the corresponding region, differencebetween the first virtual boundary and a starting point of thecorresponding region is signalled directly at the encoder side or parsedat the decoder side.

In one embodiment, if the first syntax is true, one or more secondsyntaxes are signalled at the encoder side or parsed at the decoder sideto indicate locations of said one or more virtual boundaries, and thelocations of said one or more virtual boundaries are measured in termsof width and/or height of processing unit. For example, the processingunit is set to a region comprising a picture, a slice, a tile, a CTU(coding tree unit), a CU (coding unit), a PU (prediction unit), a TU(transform unit), a pre-defined value, or a combination thereof.

In one embodiment, if a target corresponding region have same virtualboundaries as a previous corresponding region, the target correspondingregion inherits the same virtual boundaries as the previouscorresponding region. For example, the target corresponding regioncomprises a picture, a slice, a tile, a CTU (coding tree unit), a CU(coding unit), a PU (prediction unit), a TU (transform unit).Furthermore, a second syntax can be signalled at the encoder side orparsed at the decoder side to indicate whether the target correspondingregion inherits the same virtual boundaries as the previouscorresponding region.

In one embodiment, the video sequence corresponds to a 360-degreevirtual reality (VR360) video. The VR360 video comprises Equirectangularprojection (ERP), Padded Equirectangular projection (PERP), OctahedronProjection, Icosahedron Projection, Truncated Square Pyramid (TSP),Segmented Sphere Projection (SSP) or Rotated Sphere Projection (RSP).

In one embodiment, the loop filter belongs to a group comprisingde-blocking filter, SAO (Sample Adaptive Offset) filter and ALF(Adaptive Loop Filter).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an example of the boundary pixels involved inde-blocking filtering process for the vertical boundary.

FIG. 1B illustrates an example of the boundary pixels involved inde-blocking filtering process for the horizontal boundary.

FIG. 2 shows the 4 EO (Edge Offset) directional patterns (0°, 90°, 135°,and 45°) for SAO (Sample Adaptive Offset).

FIG. 3 illustrates an example of the ALF comprising a 5×5 filter and a7×7 filter, where “C” indicates a current reconstructed pixel beingfiltered.

FIG. 4 illustrates an example of 4×3 and 3×2 cubemap layout formations.

FIG. 5A illustrates an example of de-blocking filter applied to a blockof a VR360 picture in the 3×2 layout.

FIG. 5B illustrates an example of SAO processing applied to pixels of aVR360 picture in the 3×2 layout.

FIG. 5C illustrates an example of ALF process using a 5×5 or 7×7 filterfor a reconstructed VR360 picture.

FIG. 6 illustrates an example of SAO filter applied to a reconstructedpixel at the discontinuous edge.

FIG. 7A illustrates examples of de-blocking filtering process beingapplied across the discontinuous boundary or applied to a block boundaryclose to the discontinuous boundary.

FIG. 7B illustrates examples of SAO (Sample Adaptive Offset) and ALF(Adaptive Loop Filter) filtering processes being applied across thediscontinuous boundary.

FIG. 8A illustrates an example where three frames (i−1, i and i+1) havedifferent virtual boundaries as indicated by dash lines.

FIG. 8B illustrates an example of different CTUs (Coding Tree Units)that have different virtual boundaries as indicated by dash lines.

FIG. 8C illustrates an example of the starting point or end point of avirtual boundary is located inside a picture.

FIG. 9 illustrates an example of reference pixels extension for loopfiltering process across a discontinuous edge or virtual boundaryaccording to embodiments of the present invention.

FIG. 10 illustrates various examples of VR360 projection includingEquirectangular projection (ERP), Padded Equirectangular Projection(PERP), Octahedron Projection, Octahedron Projection in compact option1, and Octahedron Projection in compact option 2 are shown in FIG. 10.

FIG. 11 illustrates various examples of VR360 projection includingIcosahedron Projection, Icosahedron Projection in compact option 1, andTruncated Square Pyramid (TSP).

FIG. 12 illustrates various examples of VR360 projection includingSegmented Sphere Projection (SSP) and Rotated Sphere Projection (RSP).

FIG. 13 illustrates an exemplary flowchart of a coding system for videoaccording to an embodiment of the present invention, where a firstsyntax is signalled to indicate whether the loop filtering process isdisabled for one or more virtual boundaries in a corresponding region.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

It will be readily understood that the components of the presentinvention, as generally described and illustrated in the figures herein,may be arranged and designed in a wide variety of differentconfigurations. Thus, the following more detailed description of theembodiments of the systems and methods of the present invention, asrepresented in the figures, is not intended to limit the scope of theinvention, as claimed, but is merely representative of selectedembodiments of the invention.

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentmay be included in at least one embodiment of the present invention.Thus, appearances of the phrases “in one embodiment” or “in anembodiment” in various places throughout this specification are notnecessarily all referring to the same embodiment.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. Oneskilled in the relevant art will recognize, however, that the inventioncan be practiced without one or more of the specific details, or withother methods, components, etc. In other instances, well-knownstructures, or operations are not shown or described in detail to avoidobscuring aspects of the invention.

The illustrated embodiments of the invention will be best understood byreference to the drawings, wherein like parts are designated by likenumerals throughout. The following description is intended only by wayof example, and simply illustrates certain selected embodiments ofapparatus and methods that are consistent with the invention as claimedherein.

In the description like reference numbers appearing in the drawings anddescription designate corresponding or like elements among the differentviews.

As mentioned before, when an in-loop filter is applied to adiscontinuous boundary in VR360 videos, the filtering process for areconstructed pixel on one side of the discontinuous boundary may needto use one or more reconstructed pixels on the other side of thediscontinuous boundary (referred as unexpected pixels). Due to thediscontinuity between the pixels on two sides of the discontinuousboundary, use of the unexpected pixels for the in-loop filteringprocessing may cause noticeable artefacts. Therefore, according to amethod of the present invention, the in-loop filtering process isdisabled or a smaller size filter is used if the in-loop filteringprocess is across the discontinuous boundary. The discontinuous boundaryor edge in VR360 video or PIP is also referred as virtual boundary inthis disclosure. The in-loop filter may be referred as loop filter inthis disclosure. The in-loop filtering process may be referred as loopfiltering process in this disclosure.

FIG. 7A illustrates de-blocking filtering process being applied acrossthe discontinuous boundary 705. In FIG. 7A, the de-blocking filteringprocess 710 is applied to a current block 712, where the block boundaryis aligned with the discontinuous boundary 705. The de-blockingfiltering process for the current block 712 involves unexpected pixelsas indicated by the dots-filled area 714. Since the de-blockingfiltering process is applied across the discontinuous boundary, themethod according to the present invention disables the de-blockingfiltering process for the current block. The de-blocking filteringprocess 720 is applied to a current block 722, where the discontinuousboundary 705 is located inside the current block. The de-blockingfiltering process for the current block 722 may involve unexpectedpixels, where some of pixels in the current block may be on a differentside of the virtual boundary from the neighbouring reference block asindicated by the dots-filled area 724. A method according to the presentinvention disables the de-blocking filtering process for the currentblock or uses a de-blocking filter with a smaller filter size. Inaddition, when the virtual boundary is located inside a neighbouringreference block, a method according to the present invention disablesthe de-blocking filtering process for the current block or uses ade-blocking filter with a smaller filter size. In the HEVC, thede-blocking filter may use up to 4 pixels on each side of the blockboundary. According to embodiments of the present invention, thede-blocking filter may use less pixels on at least one side of the blockboundary.

The de-blocking filter may be applied to a block such as the transformblock boundary, sub-block boundary or other types of block. Accordingly,in one embodiment, the loop filtering process is disabled for a block(e.g. a sub-block or a transform block) if the block (e.g. a sub-blockedge or a transform block edge associated with the sub-block or thetransform block for the de-blocking filter) is aligned with the virtualboundary or the virtual boundary is located inside the block orneighbouring block.

In FIG. 7B, the SAO filtering process 730 is applied to a current pixel732 adjacent to the discontinuous boundary 705. The SAO filteringprocess for the current pixel 732 involves unexpected pixels asindicated by the dots-filled squares 734. Since the SAO filteringprocess is applied across the discontinuous boundary, the methodaccording to the present invention disables the SAO filtering processfor the current pixel. In FIG. 7B, the ALF filtering process 740 isapplied to a current pixel 742 adjacent to the discontinuous boundary705. The ALF filtering process for the current pixel 742 involvesunexpected pixels as indicated by the dots-filled squares 744. Since theALF filtering process is applied across the discontinuous boundary, themethod according to the present invention disables the ALF filteringprocess for the current pixel or use a smaller ALF if the smaller ALF isavailable. For example, if both 7×7 and 5×5 ALF are available, when the7×7 ALF is across the virtual boundary, the 5×5 ALF may be used. The ALFfiltering process includes determination of filter coefficients andapplying the filter. While, de-blocking, SAO and ALF in-loop filters areused as examples for the method of disabling in-loop filtering processacross the discontinuous boundary, the method may also be applied toother types of in-loop filtering process.

According to embodiments of the present invention, a syntax (e.g.control flag or enable flag) can be transmitted in the bitstream at asyntax level such as the SPS, PPS, APS, slice, tile, picture, CTU, CU,PU or TU level to indicate whether the filters are disabled for virtualboundaries in the corresponding region (e.g. picture, slice, tile, CTU,CU, TU or PU). For example, a control flagsps_loop_filter_disabled_across_virtual_boundaries_flag can be signalledin the sequence level to indicate whether the filters are disabled forvirtual boundaries in the frames of the sequence.

The virtual boundaries can be different in different pictures, slices,tiles, CTUs, CUs, PUs or TUs. For example, three frames (i−1, i and i+1)are shown in FIG. 8A, where the three frames have different virtualboundaries as indicated by dash lines. FIG. 8B illustrates an example ofdifferent CTUs (i.e., 840, 842, 844 and 846) that have different virtualboundaries as indicated by dash lines.

In the following, various syntax structures according to embodiments ofthe present invention are disclosed.

Syntax Structure Design I

In one embodiment, if the syntax (e.g. control flag or enable flag) istrue, then the in-loop filters are disabled across the virtualboundaries; and if the syntax (e.g. control flag or enable flag) isfalse, then the in-loop filters are not disabled when the reconstructedfilter unit is across the virtual boundaries.

In one embodiment, if the syntax (e.g. an control flag or enable flag)is equal to True, two syntaxes can be also signalled in the bitstream toindicate the number of the vertical and horizontal virtual boundaries,respectively. If the number of vertical virtual boundaries is greaterthan 0, the locations of all of the vertical virtual boundaries aresignalled in the bitstream. Similarly, if the number of horizontalvirtual boundaries is greater than 0, the locations of all of thehorizontal virtual boundaries are signalled in the bitstream.

An exemplary SPS syntax table incorporating an embodiment of the presentinvention is shown in Table 2.

TABLE 2 Descriptor seq_parameter_set_rbsp( ) { ...sps_loop_filter_disabled_across_virtual_boundaries_flag u(1) if(sps_loop_filter_disabled_across_virtual_boundaries_flag ) {sps_num_ver_virtual_boundaries ue(v) if( sps_num_ver_virtual_boundaries!= 0 ) { for( i = 0; i < sps_num_ver_virtual_boundaries; i++ ) {sps_virtual_boundaries_pos_x[ i ] ue(v) } }sps_num_hor_virtual_boundaries ue(v) if( sps_num_hor_virtual_boundaries!= 0 ) { for( i = 0; i < sps_num_hor_virtual_boundaries; i++ ) {sps_virtual_boundaries_pos_y[ i ] ue(v) } } } ... }

Since the virtual boundaries are not always set from the leftmostposition to the rightmost position of a region (e.g. picture, slice,tile, CTU, CU, PU, or TU) or from the topmost positions to thebottommost positions of a region. The starting point or end point of avirtual boundary can locate inside a picture. For example, the startingpoint or end point of a virtual boundary is located inside a picture asshown in FIG. 8C, where the vertical virtual boundary 852 has a top endinside the picture (i.e., in the middle of the picture) while thehorizontal virtual boundary is from the left side to the right side ofthe picture. Therefore, the virtual boundary starting and endingpositions are also specified in the syntax Table 3.

In another embodiment, if the syntax (i.e., control flag or enable flag)is equal to True, two syntaxes can be also signalled in the bitstream toindicate the number of the vertical and horizontal virtual boundaries,respectively. If the number of vertical virtual boundaries is greaterthan 0, the x position and y starting point and y ending point for eachvertical virtual boundary are signalled in the bitstream. If the numberof horizontal virtual boundaries is greater than 0, the y position and xstarting point and x ending point for each horizontal virtual boundaryare signalled in the bitstream.

An exemplary SPS syntax table incorporating the above embodiment of thepresent invention is shown in Table 3.

TABLE 3 Descriptor seq_parameter_set_rbsp( ) { ...sps_loop_filter_disabled_across_virtual_boundaries_flag u(1) if(sps_loop_filter_disabled_across_virtual_boundaries_flag ) {sps_num_ver_virtual_boundaries ue(v) if( sps_num_ver_virtual_boundaries!= 0 ) { for( i = 0; i < sps_num_ver_virtual_boundaries; i++ ) {sps_virtual_boundaries_pos_x[ i ] ue(v)sps_virtual_boundaries_start_pos_y[ i ] ue(v)sps_virtual_boundaries_end_pos_y[ i ] ue(v) } }sps_num_hor_virtual_boundaries ue(v) if( sps_num_hor_virtual_boundaries!= 0 ) { for( i = 0; i < sps_num_hor_virtual_boundaries; i++ ) {sps_virtual_boundaries_pos_y[ i ] ue(v)sps_virtual_boundaries_start_pos_x[ i ] ue(v)sps_virtual_boundaries_end_pos_x[ i ] ue(v) } } } ... }

In another embodiment, the length of the virtual boundaries is fixed. Inthis case, the above syntax table can be changed as shown in Table 4.Again, a syntax (e.g. control flag or enable flag) can be transmitted inthe bitstream at the SPS, PPS, APS, slice, tile, picture, CTU, CU, PU orTU level to indicate whether the in-loop filters are disabled forvirtual boundaries. If the syntax is true, then the in-loop filters aredisabled when the reconstructed filter unit is across the virtualboundaries. If the syntax is false, then the in-loop filters are notdisabled when the reconstructed filter unit is across the virtualboundaries.

If the syntax (e.g. control flag or enable flag) is equal to true, thefollowing syntax can be also transmitted in the bitstream. Two syntaxescan be transmitted into bitstream to indicate the number of the verticaland horizontal virtual boundaries are set, respectively. If the numberof vertical virtual boundaries is greater than 0, the starting points (xpositions and y positions) for each vertical virtual boundary aretransmitted into bitstream. If the number of horizontal virtualboundaries is greater than 0, the starting points (x positions and ypositions) for each horizontal virtual boundary are transmitted intobitstream.

TABLE 4 Descriptor seq_parameter_set_rbsp( ) { ...sps_loop_filter_disabled_across_virtual_boundaries_flag u(1) if(sps_loop_filter_disabled_across_virtual_boundaries_flag ) {sps_num_ver_virtual_boundaries ue(v) if( sps_num_ver_virtual_boundaries!= 0 ) { for( i = 0; i < sps_num_ver_virtual_boundaries; i++ ) {sps_ver_virtual_boundaries_pos_x[ i ] ue(v)sps_ver_virtual_boundaries_pos_y[ i ] ue(v) } }sps_num_hor_virtual_boundaries ue(v) if( sps_num_hor_virtual_boundaries!= 0 ) { for( i = 0; i < sps_num_hor_virtual_boundaries; i++ ) {sps_hor_virtual_boundaries_pos_x[ i ] ue(v)sps_hor_virtual_boundaries_pos_y[ i ] ue(v) } } } ... }

Syntax Structure Design II

A more flexible syntax structure to signal various types of virtualboundaries is also disclosed. The virtual boundaries are not always setfrom the leftmost positions to the rightmost positions of a region(picture, slice, tile, CTU, CU, PU, TU) or from the topmost positions tothe bottommost positions of a region.

Two location starting point and ending point for each virtual boundaryare signalled in the bitstream so that the virtual boundaries can be setas rectangle boxes or straight lines. The stating point indicates theleft-top position of the box and the ending point indicates theright-bottom position of the box.

If the syntax (i.e., control flag or enable flag) is equal to True, thefollowing syntax can be also signalled in the bitstream. One syntax canbe signalled in the bitstream to indicate the number of the virtualboundaries. If the number of virtual boundaries is greater than 0, thelocations of the starting points and the end points of all of thevirtual boundaries are signalled in the bitstream.

An exemplary syntax table incorporating the above embodiment is shown inTable 5.

TABLE 5 Descriptor seq_parameter_set_rbsp( ) { ...sps_loop_filter_disabled_across_virtual_boundaries_flag u(1) if(sps_loop_filter_disabled_across_virtual_boundaries_flag ) {sps_num_virtual_boundaries ue(v) if( sps_num_virtual_boundaries != 0 ) {for( i = 0; i < sps_num_virtual_boundaries; i++ ) {sps_virtual_boundaries_start_pos_x[ i ] ue(v)sps_virtual_boundaries_start_pos_y[ i ] ue(v)sps_virtual_boundaries_end_pos_x[ i ] ue(v)sps_virtual_boundaries_end_pos_y[ i ] ue(v) } } } ... }

In another example, the syntax structure is similar to that in Table 5.However, the virtual boundaries can be signalled by locations of theircorresponding starting points and the offset values between startingpoints and ending points:

virtual_boundaries_end_pos_x[i]=virtual_boundaries_start_pos_x[i]+virtual_boundaries_offset_x[i],

virtual_boundaries_end_pos_y[i]=virtual_boundaries_start_pos_y[i]+virtual_boundaries_offset_y[i],

where i=0, . . . num_virtual_boundaries−1.

Again, a syntax (e.g. control flag or enable flag) can be transmitted inbitstream at the SPS, PPS, APS, slice, tile, picture, CTU, CU, PU or TUlevel to indicate whether the in-loop filters are disabled for virtualboundaries. If the syntax is true, then the in-loop filters are disabledwhen the reconstructed filter unit is across the virtual boundaries. Ifthe syntax is false, then the in-loop filters are not disabled when thereconstructed filter unit is across the virtual boundaries.

If the syntax (e.g. control flag or enable flag) is equal to true, thefollowing syntax can be also signalled in bitstream. One syntax can besignalled in the bitstream to indicate the number of the virtualboundaries existing in the corresponding region. If the number ofvirtual boundaries is greater than 0, the locations of the startingpoints and the offset values of all of the virtual boundaries aresignalled in the bitstream.

An exemplary syntax table incorporating the above embodiment is shown inTable 6.

TABLE 6 Descriptor seq_parameter_set_rbsp( ) { ...sps_loop_filter_disabled_across_virtual_boundaries_flag u(1) if(sps_loop_filter_disabled_across_virtual_boundaries_flag ) {sps_num_virtual_boundaries ue(v) if( sps_num_virtual_boundaries != 0 ) {for( i = 0; i < sps_num_virtual_boundaries; i++ ) {sps_virtual_boundaries_start_pos_x[ i ] ue(v)sps_virtual_boundaries_start_pos_y[ i ] ue(v)sps_virtual_boundaries_offset_x[ i ] se(v)sps_virtual_boundaries_offset_y[ i ] se(v) } } } ... }

Syntax Structure Design III

For some VR projection pictures, the layout may include virtualboundaries in various angles beside the vertical and horizontaldirections and multiple virtual boundaries can form a non-square shape,such as a triangle or a rectangle. Furthermore, the virtual boundary canbe a straight line or a shape such as a circle. According to someembodiments of the present invention, the syntax structure is designedto support such cases.

Again, a syntax (e.g. control flag or enable flag) can be transmitted inbitstream at the SPS, PPS, APS, slice, tile, picture, CTU, CU, PU or TUlevel to indicate whether the in-loop filters are disabled for virtualboundaries. If the syntax is true, then the in-loop filters are disabledwhen the reconstructed filter unit is across the virtual boundaries. Ifthe syntax is false, then the in-loop filters are not disabled when thereconstructed filter unit is across the virtual boundaries.

In one embodiment, if the syntax (e.g. control flag or enable flag) isequal to True, the following syntax can be also signalled in thebitstream. For example, one syntax can be signalled in the bitstream toindicate the number of the virtual boundaries. If the number of virtualboundaries is greater than 0, a syntax (e.g. shape flag) can besignalled in the bitstream to indicate the shape of each virtualboundary. For example, if the shape flag is equal to a first value (e.g.0), the virtual boundary is a straight line. The location of thestarting and end points are signalled in the bitstream. If the shapeflag is equal to a second value (e.g. 1), the virtual boundary is acircle. The position of the centre of the circle and the radius of thecircle can be signalled in the bitstream.

An exemplary syntax table corresponding to the above embodiment based onsyntax table in Table 5 for syntax structure II is shown in Table 7.

TABLE 7 Descriptor seq_parameter_set_rbsp( ) { ...sps_loop_filter_disabled_across_virtual_boundaries_flag u(1) if(sps_loop_filter_disabled_across_virtual_boundaries_flag ) {sps_num_virtual_boundaries ue(v) if( sps_num_virtual_boundaries != 0 ) {for( i = 0; i < sps_num_virtual_boundaries; i++ ) {sps_virtual_boundaries_shape[ i ] u(1) if (sps_virtual_boundaries_shape[i ] == 0 ) { // straight line sps_virtual_boundaries_start_pos_x[ i ]ue(v) sps_virtual_boundaries_start_pos_y[ i ] ue(v)sps_virtual_boundaries_end_pos_x[ i ] ue(v)sps_virtual_boundaries_end_pos_y[ i ] ue(v) } if(sps_virtual_boundaries_shape[ i ] == 1 ) { // circlesps_virtual_boundaries_center_pos_x[ i ] ue(v)sps_virtual_boundaries_centerpos_y[ i ] ue(v)sps_virtual_boundaries_radius[ i ] ue(v) } } } } ... }

An exemplary syntax table corresponding to the above embodiment based onsyntax table in Table 6 for syntax structure II is shown in Table 8.

TABLE 8 Descriptor seq_parameter_set_rbsp( ) { ...sps_loop_filter_disabled_across_virtual_boundaries_flag u(1) if(sps_loop_filter_disabled_across_virtual_boundaries_flag ) {sps_num_virtual_boundaries ue(v) if( sps_num_virtual_boundaries != 0 ) {for( i = 0; i < sps_num_virtual_boundaries; i++ ) {sps_virtual_boundaries_shape[ i ] u(1) if (sps_virtual_boundaries_shape[i ] == 0 ) { // straight line sps_virtual_boundaries_start_pos_x[ i ]ue(v) sps_virtual_boundaries_start_pos_y[ i ] ue(v)sps_virtual_boundaries_offset_x[ i ] se(v)sps_virtual_boundaries_offset_y[ i ] se(v) } if(sps_virtual_boundaries_shape[ i ] == 1 ) { // circlesps_virtual_boundaries_center_pos_x[ i ] ue(v)sps_virtual_boundaries_centerpos_y[ i ] ue(v)sps_virtual_boundaries_radius[ i ] ue(v) } } } } ... }

Reducing the Bit Number for Signalling

In order to reduce the bit number in the bitstream, the locations of thevirtual boundaries can be derived from the previous virtual boundariesand the difference values between previous and current virtualboundaries.

According to one method of the present invention, only the differencevalues are signalled in the bitstream. The locations of the firstvirtual boundary can be derived as follows:

virtual_boundaries_pos_x[0]=0+virtual_boundaries_diff_x[0],

virtual_boundaries_pos_y[0]=0+virtual_boundaries_diff_y[0].

For the first virtual boundary, the location may also be derived fromthe starting positions of current region:

virtual_boundaries_pos_x[0]=(x position of starting point of currentregion)+virtual_boundaries_diff_x[0],

virtual_boundaries_pos_y[0]=(y position of starting point of currentregion)+virtual_boundaries_diff_y[0].

The locations of other virtual boundaries can be derived as follows:

virtual_boundaries_pos_x[i]=virtual_boundaries_pos_x[i−1]+virtual_boundaries_diff_x[i],

virtual_boundaries_pos_y[i]=virtual_boundaries_pos_y[i−1]+virtual_boundaries_diff_y[i].

where i=1, . . . num_virtual_boundaries−1

This method can be combined with the syntax structure I, II and III toreduce the bit number of bitstream

An exemplary syntax table incorporating the above embodiment to reducethe bit number is shown in Table 9.

TABLE 9 Descriptor seq_parameter_set_rbsp( ) { ...sps_loop_filter_disabled_across_virtual_boundaries_flag u(1) if(sps_loop_filter_disabled_across_virtual_boundaries_flag ) {sps_num_ver_virtual_boundaries ue(v) if( sps_num_ver_virtual_boundaries!= 0 ) { for( i = 0; i < sps_num_ver_virtual_boundaries; i++ ) {sps_virtual_boundaries_diff_x[ i ] // difference se(v) } }sps_num_hor_virtual_boundaries ue(v) if( sps_num_hor_virtual_boundaries!= 0 ) { for( i = 0; i < sps_num_hor_virtual_boundaries; i++ ) {sps_virtual_boundaries_diff_y[ i ] // difference se(v) } } } ... }

According to another embodiment, the absolute location of the firstvirtual boundary and the difference values of other virtual boundariesare signalled in the bitstream. The location of the other virtualboundaries can be derived from the previous virtual boundaries and thedifference values between previous and current virtual boundaries.

Except for the first virtual boundary, the locations of other virtualboundaries can be derived as before as shown below.

virtual_boundaries_pos_x[i]=virtual_boundaries_pos_x[i−1]+virtual_boundaries_diff_x[i],

virtual_boundaries_pos_y[i]=virtual_boundaries_pos_y[i−1]+virtual_boundaries_diff_y[i].

where i=1, . . . num_virtual_boundaries−1

An exemplary syntax table incorporating the above embodiment to reducethe bit number is shown in Table 10.

TABLE 10 Descriptor seq_parameter_set_rbsp( ) { ...sps_loop_filter_disabled_across_virtual_boundaries_flag u(1) if(sps_loop_filter_disabled_across_virtual_boundaries_flag ) {sps_num_ver_virtual_boundaries ue(v) if( sps_num_ver_virtual_boundaries!= 0 ) { sps_virtual_boundaries_pos_x[ 0 ] ue(v) for( i = 1; i <sps_num_ver_virtual_boundaries; i++ ) { sps_virtual_boundaries_diff_x[ i] // difference se(v) } } sps_num_hor_virtual_boundaries ue(v) if(sps_num_hor_virtual_boundaries != 0 ) { sps_virtual_boundaries_pos_y[ 0] ue(v) for( i = 1; i < sps_num_hor_virtual_boundaries; i++ ) {sps_virtual_boundaries_diff_y[ i ] // difference se(v) } } } ... }

To reduce the bit number, the locations of the virtual boundaries can beset to multiple of minimum width/height of processing unit. Therefore,the locations of virtual boundaries can be signalled in the bitstream inunits of minimum processing unit.

For example, the minimum processing unit in the emerging VVC (VersatileVideo Coding) standard is 4×4 block; therefore, the location of thevirtual boundaries is set to multiple of 4.

To further reduce the bit number, the locations of virtual boundariescould be signalled in the bitstream in units of slice, tile, CTU, CU,PU, TU, other predefined values or a combination thereof. For example,the location of a vertical virtual boundary can be 3-CTU width plus5-block width.

This method can be combined with the syntax structure I, II and III toreduce the bit number of bitstream. This method can also be combinedwith other bit number reduction methods.

The bit number reduction method can also be applied to the offset anddifference values in the syntax structures.

The virtual boundary position can be inherited from previous region(e.g. picture, slice, tile, CTU, CU, TU, PU, etc.) and, therefore, thenumber of bits can be reduced for the current region (e.g. picture,slice, tile, CTU, CU, TU, PU, etc.). For example, if the positions ofvirtual boundaries in the current frame are the same as previous frame,the virtual boundaries can be inherited from the previous frame. Inanother example, if the positions of virtual boundaries in the currentCTU are the same as the previous CTU, the virtual boundaries can beinherited from the previous CTU. For the current region, one additionsyntax (e.g. sps_virtual_boundary_inherit_flag) can be used to identifywhether the virtual boundaries are inherited from a previous region ornot.

An exemplary syntax table incorporating the above embodiment to reducethe bit number is shown in Table 11.

TABLE 11 Descriptor seq_parameter_set_rbsp( ) { ...sps_loop_filter_disabled_across_virtual_boundaries_flag u(1) if(sps_loop_filter_disabled_across_virtual_boundaries_flag ) {sps_virtual_boundary_inherit_flag u(1) if (!Sps_virtual_boundary_inherit) { sps_num_ver_virtual_boundaries ue(v) if(sps_num_ver_virtual_boundaries != 0 ) { for( i = 0; i <sps_num_ver_virtual_boundaries; i++ ) { sps_virtual_boundaries_pos_x[ i] ue(v) } } sps_num_hor_virtual_boundaries ue(v) if(sps_num_hor_virtual_boundaries != 0 ) { for( i = 0; i <sps_num_hor_virtual_boundaries; i++ ) { sps_virtual_boundaries_pos_y[ i] ue(v) } } } } ... }

FIG. 9 illustrates an example of reference pixels extension 910 for loopfiltering process across a discontinuous edge or virtual boundaryaccording to embodiments of the present invention. In FIG. 9, pixelsfrom the top sub-frame are extended to form alternative reference pixels(labelled as dot-filled area 1) and pixels from the bottom sub-frame areextended to form alternative reference pixels (labelled as dot-filledarea 2). In FIG. 9, the virtual boundary (912 a and 912 b) are shown forthe top sub-frame and the bottom sub-frame. When the pixels on the sameside of the virtual boundary are extended to form the alternativereference pixels, the nearest pixels in the current sub-frame are used.In other words, the bottom line of the top sub-frame is extendeddownward to form the reference pixel area 1 and the top line of thebottom sub-frame is extended upward to form the reference pixel area 2.When a reference pixel from the other side of the discontinuous edge orvirtual boundary is required for the loop filtering process, the nearestpixels in the current sub-frame (i.e., on the same side of discontinuousedge/virtual boundary as the current pixel) are used as the alternativereferenced pixels. In FIG. 9, the VR360 picture consists of a topsub-frame and a bottom sub-frame. As is understood, the 3×2 cubemaplayout is intended as an example to illustrate the reference pixelextension according to embodiment of the present invention.

The reference pixel extension can be applied to other VR360 layoutformats, such as the layout formats derived from OctaHedron Projection(OHP), icosahedron projection (ISP), Segmented Sphere Projection (SSP)and Rotated Sphere Projection (RSP). There may be more than one virtualboundaries in the VR360 pictures. Furthermore, the virtual boundariesmay be in other directions instead of vertical/horizontal. When the loopfiltering process involves unexpected reference pixels (i.e., referencepixels on the other side of the virtual boundary), the nearest pixels onthe same side as the current reconstructed pixel to be filtered can beextended to form the alternative reference pixels.

The filtering control (i.e., enable or disable) across virtual boundaryhas been shown based on the 3×2 cubemap layout. However, the filteringprocess across virtual boundaries described above is also applicable toother VR formats such as OctaHedron Projection (OHP), icosahedronprojection (ISP), Segmented Sphere Projection (SSP) and Rotated SphereProjection (RSP). Pictures corresponding to Equirectangular projection(ERP) 1010, Padded Equirectangular Projection (PERP) 1020, OctahedronProjection 1030, Octahedron Projection 1040 in compact option 1, andOctahedron Projection 1050 in compact option 2 are shown in FIG. 10.Pictures corresponding to Icosahedron Projection 1110, IcosahedronProjection 1120 in compact option 1, and Truncated Square Pyramid (TSP)1130 are shown in FIG. 11. Pictures corresponding to Segmented SphereProjection (SSP) 1210 and Rotated Sphere Projection (RSP) 1220 are shownin FIG. 12.

This method is not only applicable to the de-blocking filter, ALF andSAO filters but also applicable to the other filters.

FIG. 13 illustrates an exemplary flowchart of a coding system for videoaccording to an embodiment of the present invention, where a firstsyntax is signalled to indicate whether the loop filtering process isdisabled for one or more virtual boundaries in a corresponding region.The steps shown in the flowchart, as well as other following flowchartsin this disclosure, may be implemented as program codes executable onone or more processors (e.g., one or more CPUs) at the encoder sideand/or the decoder side. The steps shown in the flowchart may also beimplemented based hardware such as one or more electronic devices orprocessors arranged to perform the steps in the flowchart. According tothis method, a first syntax is signalled in a bitstream at an encoderside or the first syntax is parsed from the bitstream at a decoder sidein step 1310, wherein the first syntax indicates whether a loopfiltering process is disabled for one or more virtual boundaries in acorresponding region. A reconstructed filter unit for a currentreconstructed pixel in a picture is received in step 1320, wherein thereconstructed filter unit is associated with a loop filter and thereconstructed filter unit comprises reconstructed pixels for applying aloop filtering process associated with the loop filter to the currentreconstructed pixel. When the first syntax is true, the loop filterprocessing is disabled when the reconstructed filter unit is across saidone or more virtual boundaries in the corresponding region. When thefirst syntax is false, the loop filter processing is not disabled whenthe reconstructed filter unit is across the virtual boundary.

The flowchart shown above is intended for serving as examples toillustrate embodiments of the present invention. A person skilled in theart may practice the present invention by modifying individual steps,splitting or combining steps with departing from the spirit of thepresent invention.

The above description is presented to enable a person of ordinary skillin the art to practice the present invention as provided in the contextof a particular application and its requirement. Various modificationsto the described embodiments will be apparent to those with skill in theart, and the general principles defined herein may be applied to otherembodiments. Therefore, the present invention is not intended to belimited to the particular embodiments shown and described, but is to beaccorded the widest scope consistent with the principles and novelfeatures herein disclosed. In the above detailed description, variousspecific details are illustrated in order to provide a thoroughunderstanding of the present invention. Nevertheless, it will beunderstood by those skilled in the art that the present invention may bepracticed.

Embodiment of the present invention as described above may beimplemented in various hardware, software codes, or a combination ofboth. For example, an embodiment of the present invention can be one ormore electronic circuits integrated into a video compression chip orprogram code integrated into video compression software to perform theprocessing described herein. An embodiment of the present invention mayalso be program code to be executed on a Digital Signal Processor (DSP)to perform the processing described herein. The invention may alsoinvolve a number of functions to be performed by a computer processor, adigital signal processor, a microprocessor, or field programmable gatearray (FPGA). These processors can be configured to perform particulartasks according to the invention, by executing machine-readable softwarecode or firmware code that defines the particular methods embodied bythe invention. The software code or firmware code may be developed indifferent programming languages and different formats or styles. Thesoftware code may also be compiled for different target platforms.However, different code formats, styles and languages of software codesand other means of configuring code to perform the tasks in accordancewith the invention will not depart from the spirit and scope of theinvention.

The invention may be embodied in other specific forms without departingfrom its spirit or essential characteristics. The described examples areto be considered in all respects only as illustrative and notrestrictive. The scope of the invention is therefore, indicated by theappended claims rather than by the foregoing description. All changeswhich come within the meaning and range of equivalency of the claims areto be embraced within their scope.

1. A method of coding a video sequence, wherein pictures from the video sequence include one or more discontinuous edges, the method comprising: signalling a first syntax in a bitstream at an encoder side or parsing the first syntax from the bitstream at a decoder side, wherein the first syntax indicates whether a loop filtering process is disabled for one or more virtual boundaries in a corresponding region; receiving a reconstructed filter unit in a current picture, wherein the reconstructed filter unit is associated with a loop filter and the reconstructed filter unit comprises reconstructed pixels for applying the loop filtering process associated with the loop filter to a current reconstructed pixel; wherein when the first syntax is true, the loop filter processing is disabled when the reconstructed filter unit is across said one or more virtual boundaries in the corresponding region; and when the first syntax is false, the loop filter processing is not disabled when the reconstructed filter unit is across the virtual boundary in the corresponding region.
 2. The method of claim 1, wherein the first syntax is signalled in or parsed from the bitstream at a syntax level comprising SPS (Sequence Parameter Set), PPS (Picture Parameter Set), APS (Application Parameter Set), slice, tile, picture, CTU (Coding Tree Unit), CU (Coding Unit), PU (Prediction Unit) or TU (Transform Unit) level for the corresponding region.
 3. The method of claim 1, wherein if the first syntax is true, one or more second syntaxes are signalled at the encoder side or parsed at the decoder side, and wherein said one or more second syntaxes indicate virtual boundary information in the corresponding region.
 4. The method of claim 3, wherein said one or more second syntaxes comprise a first number to indicate a number of vertical virtual boundaries and a second number to indicate a number of horizontal virtual boundaries in the corresponding region.
 5. The method of claim 4, wherein each vertical virtual boundary is from a top edge to a bottom edge of the corresponding region and each horizontal virtual boundary is from a left edge to a right edge of the corresponding region; when the first number is greater than 0, locations of each vertical virtual boundary are transmitted in or parsed from the bitstream; and when the second number is greater than 0, locations of each horizontal virtual boundary are transmitted in or parsed from the bitstream.
 6. The method of claim 4, wherein the vertical virtual boundaries are not necessarily from a top edge to a bottom edge of the corresponding region and the horizontal virtual boundaries are not necessarily from a left edge to a right edge of the corresponding region; when the first number is greater than 0, locations of x-position, y starting position and y ending position for each vertical virtual boundary are transmitted in or parsed from the bitstream; and when the second number is greater than 0, locations of y-position, x starting position and x ending position for each horizontal virtual boundary are transmitted in or parsed from the bitstream.
 7. The method of claim 4, wherein length of the vertical virtual boundaries and the length of the horizontal virtual boundaries is fixed; when the first number is greater than 0, location of starting point for each vertical virtual boundary is transmitted in or parsed from the bitstream; and when the second number is greater than 0, the location of starting point for each horizontal virtual boundary is transmitted in or parsed from the bitstream.
 8. The method of claim 1, wherein if the first syntax is true, one or more second syntaxes are signalled at the encoder side or parsed at the decoder side, and wherein said one or more second syntaxes indicate a number of said one or more virtual boundaries in the corresponding region.
 9. The method of claim 8, wherein when the number of said one or more virtual boundaries is greater than 0, locations of starting points and ending points of said one or more virtual boundaries are transmitted in the bitstream.
 10. The method of claim 9, wherein said one or more virtual boundaries correspond to one or more rectangle boxes and starting points and ending points correspond to left-top positions and right-bottom positions of said one or more rectangle boxes.
 11. The method of claim 8, wherein when the number of said one or more virtual boundaries is greater than 0, locations of starting points and offset values between the starting points and corresponding ending points of said one or more virtual boundaries are transmitted in or parsed from the bitstream.
 12. The method of claim 1, wherein one or more second syntaxes are signalled at the encoder side or parsed at the decoder side to indicate difference values between a current virtual boundary and a previous virtual boundary.
 13. The method of claim 12, wherein when the current virtual boundary is a first virtual boundary in the corresponding region, absolute position of the first virtual boundary is signalled directly at the encoder side or parsed directly at the decoder side.
 14. The method of claim 12, wherein when the current virtual boundary is a first virtual boundary in the corresponding region, difference between the first virtual boundary and a starting point of the corresponding region is signalled directly at the encoder side or parsed at the decoder side.
 15. The method of claim 1, wherein if the first syntax is true, one or more second syntaxes are signalled at the encoder side or parsed at the decoder side to indicate locations of said one or more virtual boundaries, and wherein the locations of said one or more virtual boundaries are measured in terms of width and/or height of processing unit.
 16. The method of claim 15, wherein a processing unit is set to a region comprising a picture, a slice, a tile, a CTU (coding tree unit), a CU (coding unit), a PU (prediction unit), a TU (transform unit), or a pre-defined value.
 17. The method of claim 1, wherein if a target corresponding region have same virtual boundaries as a previous corresponding region, the target corresponding region inherits the same virtual boundaries as the previous corresponding region.
 18. The method of claim 17, wherein the target corresponding region comprises a picture, a slice, a tile, a CTU (coding tree unit), a CU (coding unit), a PU (prediction unit), a TU (transform unit).
 19. The method of claim 17, wherein a second syntax is signalled at the encoder side or parsed at the decoder side to indicate whether the target corresponding region inherits the same virtual boundaries as the previous corresponding region.
 20. The method of claim 1, wherein the loop filter belongs to a group comprising de-blocking filter, SAO (Sample Adaptive Offset) filter and ALF (Adaptive Loop Filter).
 21. An apparatus for coding a video sequence, wherein pictures from the video sequence include one or more discontinuous edges, the apparatus comprising one or more electronic devices or processors configured to: signal a first syntax in a bitstream at an encoder side or parsing the first syntax from the bitstream at a decoder side, wherein the first syntax indicates whether a loop filtering process is disabled for one or more virtual boundaries in a corresponding region; receive a reconstructed filter unit in a current picture, wherein the reconstructed filter unit is associated with a loop filter and the reconstructed filter unit comprises reconstructed pixels for applying the loop filtering process associated with the loop filter to a current reconstructed pixel; wherein when the first syntax is true, the loop filter processing is disabled when the reconstructed filter unit is across said one or more virtual boundaries in the corresponding region; and when the first syntax is false, the loop filter processing is not disabled when the reconstructed filter unit is across the virtual boundary in the corresponding region. 